Data from: Differential allocation in a lekking bird: females lay larger eggs and are more likely to have male chicks when they mate with less related males

The differential allocation hypothesis predicts increased investment in offspring when females mate with high-quality males. Few studies have tested whether investment varies with mate relatedness, despite evidence that non-additive gene action influences mate and offspring genetic quality. We tested whether female lekking lance-tailed manakins (Chiroxiphia lanceolata) adjust offspring sex and egg volume in response to mate attractiveness (annual reproductive success, ARS), heterozygosity and relatedness. Across 968 offspring, the probability of being male decreased with increasing parental relatedness but not father ARS or heterozygosity. This correlation tended to diminish with increasing lay-date. Across 162 offspring, egg volume correlated negatively with parental relatedness and varied with lay-date, but was unrelated to father ARS or heterozygosity. Offspring sex and egg size were unrelated to maternal age. Comparisons of maternal half-siblings in broods with no mortality produced similar results, indicating differential allocation rather than covariation between female quality and relatedness or sex-specific inbreeding depression in survival. As males suffer greater inbreeding depression, overproducing females after mating with related males may reduce fitness costs of inbreeding in a system with no inbreeding avoidance, while biasing the sex of outbred offspring towards males may maximize fitness via increased mating success of outbred sons.

差异性分配假说（differential allocation hypothesis）预测，当雌性与高质量雄性交配时，会增加对后代的投入。尽管已有证据表明非加性基因效应（non-additive gene action）会影响配偶与后代的遗传质量，但鲜有研究检验后代投入是否随配偶亲缘关系的变化而改变。本研究以求偶场繁殖的尖尾侏儒鸟（Chiroxiphia lanceolata）为研究对象，检验雌性是否会根据配偶的吸引力（年度繁殖成功率（annual reproductive success, ARS））、杂合度（heterozygosity）以及亲缘关系，调整后代性别比例与卵体积。对968只后代的分析显示，雄性出生概率随亲本亲缘关系升高而降低，但与父亲的年度繁殖成功率或杂合度无显著关联；该相关性随产卵日期延后逐渐减弱。对162只后代的分析则表明，卵体积与亲本亲缘关系呈负相关，且随产卵日期变化，但与父亲的年度繁殖成功率或杂合度无关。后代性别与卵大小均与母体年龄无关联。对无死亡发生的窝中母本半同胞后代进行比较后得到了相似结果，这表明该现象源于差异性分配，而非雌性质量与亲缘关系间的协变关系，亦非存活过程中存在的性别特异性近交衰退（inbreeding depression）。鉴于雄性受近交衰退的影响更为显著，在不存在近交回避机制的系统中，雌性与亲缘雄性交配后过量产生雌性后代，可降低近交带来的适合度成本；而将远交后代的性别比例偏向雄性，则可通过提升远交雄性的交配成功率，最大化自身适合度。